Hybrid brake system

ABSTRACT

A braking system is disclosed. In various embodiments, the brake system includes a brake assembly; a hydraulic braking subsystem having a hydraulic brake actuator configured to operate the brake assembly; and an electric braking subsystem having an electric brake actuator configured to operate the brake assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and the benefit of, U.S. Provisional Application Ser. No. 63/085,011, filed Sep. 29, 2020 and titled “HYBRID BRAKE SYSTEM,” which is incorporated by reference herein in its entirety for all purposes.

FIELD

The present disclosure relates to aircraft wheel and brake systems and, more particularly, to systems and methods for enhancing redundancy in aircraft wheel and brake systems via hybrid brake systems having both hydraulic and electric braking subsystems.

BACKGROUND

Aircraft typically utilize brake systems on wheels to slow or stop the aircraft during landings, taxiing and emergency situations, such as, for example, a rejected takeoff (RTO), which generally refers to engagement of a brake system during an aborted takeoff and involves high braking loads over a short time period, resulting in a rapid increase in the brake temperature. The brake systems generally employ a heat sink comprising a series of friction disks, sandwiched between a pressure plate and an end plate, that may be forced into sliding contact with one another during a brake application to slow or stop the aircraft.

A typical hydraulic brake system may include, without limitation, a source of pressurized hydraulic fluid, a hydraulic actuator for exerting a force across the heat sink (e.g., across the pressure plate, the series of friction disks and the end plate), a valve for controlling a pressure level provided to the hydraulic actuator and a brake control unit for receiving inputs from a pilot and from various feedback mechanisms and for producing responsive outputs to the valve. Upon activation of the brake system (e.g., by depressing a brake pedal), a pressurized fluid is applied to the hydraulic actuator, which may comprise a piston configured to translate the pressure plate toward the end plate. A typical electric brake system includes various electromechanical counterparts to a hydraulic brake system, such as, for example, an electromechanical actuator in place of the hydraulic actuator and a source of electric power in place of the source of pressurized hydraulic fluid.

SUMMARY

A braking system is disclosed. In various embodiments, the brake system includes a brake assembly; a hydraulic braking subsystem having a hydraulic brake actuator configured to operate the brake assembly; and an electric braking subsystem having an electric brake actuator configured to operate the brake assembly.

In various embodiments, the brake assembly includes a pressure plate and an end plate and both the hydraulic brake actuator and the electric brake actuator are configured to translate the pressure plate toward the end plate. In various embodiments, the hydraulic brake actuator is one of a plurality of hydraulic brake actuators configured to translate the pressure plate toward the end plate. In various embodiments, the electric brake actuator is one of a plurality of electric brake actuators configured to translate the pressure plate toward the end plate. In various embodiments, the plurality of hydraulic brake actuators comprises four hydraulic brake actuators spaced at ninety degree intervals about the pressure plate. In various embodiments, the plurality of electric brake actuators comprises four electric brake actuators spaced at ninety degree intervals about the pressure plate.

In various embodiments, the hydraulic braking subsystem includes a hydraulic brake control unit configured to control operation of the hydraulic brake actuator. In various embodiments, the electric braking subsystem includes an electric brake control unit configured to control operation of the electric brake actuator. In various embodiments, the braking system includes an intercommunication bus between the hydraulic brake control unit and the electric brake control unit.

In various embodiments, the hydraulic brake control unit is configured to transfer operation of the braking system to the electric brake control unit following a failure occurring within the hydraulic braking subsystem. In various embodiments, a pressure transducer is configured to sense the failure, via a loss or a reduction of fluid pressure, occurring within the hydraulic braking subsystem. In various embodiments, the electric brake control unit is configured to transfer operation of the braking system to the hydraulic brake control unit following a failure occurring within the electric braking subsystem. In various embodiments, a hydraulic brake position sensor is coupled to the hydraulic brake control unit and configured to sense a brake pedal position. In various embodiments, an electric brake position sensor is coupled to the electric brake control unit and configured to sense the brake pedal position.

A redundant braking system for an aircraft is disclosed. In various embodiments, the redundant braking system includes a brake assembly having a pressure plate, an end plate, a plurality of rotor disks and a plurality of stator disks interleaved with the plurality of rotor disks, the plurality of rotor disks and the plurality of stator disks disposed between the pressure plate and the end plate; a hydraulic braking subsystem having a hydraulic brake actuator configured to compress the plurality of rotor disks against the plurality of stator disks; and an electric braking subsystem having an electric brake actuator configured to compress the plurality of rotor disks against the plurality of stator disks.

In various embodiments, the hydraulic brake actuator is one of a plurality of hydraulic brake actuators spaced at equal degree intervals about the pressure plate. In various embodiments, the electric brake actuator is one of a plurality of electric brake actuators spaced at equal degree intervals about the pressure plate.

In various embodiments, the hydraulic braking subsystem includes a hydraulic brake control unit configured to control operation of the hydraulic brake actuator and the electric braking subsystem includes an electric brake control unit configured to control operation of the electric brake actuator. In various embodiments, the hydraulic brake control unit is configured to transfer operation of the redundant braking system to the electric brake control unit following a failure occurring within the hydraulic braking subsystem. In various embodiments, the electric brake control unit is configured to transfer operation of the redundant braking system to the hydraulic brake control unit following a failure occurring within the electric braking subsystem.

The foregoing features and elements may be combined in any combination, without exclusivity, unless expressly indicated herein otherwise. These features and elements as well as the operation of the disclosed embodiments will become more apparent in light of the following description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the following detailed description and claims in connection with the following drawings. While the drawings illustrate various embodiments employing the principles described herein, the drawings do not limit the scope of the claims.

FIG. 1A illustrates an aircraft having multiple landing gear and brakes, in accordance with various embodiments;

FIG. 1B is a block diagram of a brake control unit, in accordance with various embodiments;

FIG. 1C is a schematic diagram of a brake assembly, in accordance with various embodiments; and

FIGS. 2A and 2B are functional diagrams of a hybrid or redundant braking system, in accordance with various embodiments.

DETAILED DESCRIPTION

The following detailed description of various embodiments herein makes reference to the accompanying drawings, which show various embodiments by way of illustration. While these various embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, it should be understood that other embodiments may be realized and that changes may be made without departing from the scope of the disclosure. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected, or the like may include permanent, removable, temporary, partial, full or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. It should also be understood that unless specifically stated otherwise, references to “a,” “an” or “the” may include one or more than one and that reference to an item in the singular may also include the item in the plural. Further, all ranges may include upper and lower values and all ranges and ratio limits disclosed herein may be combined.

Referring now to FIG. 1A, an aircraft 100 includes multiple landing gear systems, including a first landing gear 102 (or a port-side landing gear), a second landing gear 104 (or a nose landing gear) and a third landing gear 106 (or a starboard-side landing gear). The first landing gear 102, the second landing gear 104 and the third landing gear 106 each include one or more wheel assemblies. For example, the third landing gear 106 includes an inner wheel assembly 108 and an outer wheel assembly 110. The first landing gear 102, the second landing gear 104 and the third landing gear 106 support the aircraft 100 when the aircraft 100 is not flying, thereby enabling the aircraft 100 to take off, land and taxi without incurring damage. In various embodiments, one or more of the first landing gear 102, the second landing gear 104 and the third landing gear 106 is operationally retractable into the aircraft 100 while the aircraft 100 is in flight.

In various embodiments, the aircraft 100 further includes an avionics unit 112, which includes one or more controllers (e.g., processors) and one or more tangible, non-transitory memories capable of implementing digital or programmatic logic. In various embodiments, for example, the one or more controllers are one or more of a general purpose processor, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate array (FPGA) or other programmable logic device, discrete gate, transistor logic, or discrete hardware component, or any of various combinations thereof or the like. In various embodiments, the avionics unit 112 controls operation of various components of the aircraft 100. For example, the avionics unit 112 controls various parameters of flight, such as an air traffic management systems, auto-pilot systems, auto-thrust systems, crew alerting systems, electrical systems, electronic checklist systems, electronic flight bag systems, engine systems flight control systems, environmental systems, hydraulics systems, lighting systems, pneumatics systems, traffic avoidance systems, trim systems, brake systems and the like.

In various embodiments, the aircraft 100 further includes a brake control unit (BCU) 120. With brief reference now to FIG. 1B, the BCU 120 includes one or more controllers 115 (e.g., processors) and one or more memories 116 (e.g., tangible, non-transitory memories) capable of implementing digital or programmable logic. In various embodiments, for example, the one or more controllers 115 is one or more of a general purpose processor, DSP, ASIC, FPGA, or other programmable logic device, discrete gate, transistor logic, or discrete hardware component, or any of various combinations thereof or the like, and the one or more memories 116 is configured to store instructions that are implemented by the one or more controllers 115 for performing various functions, such as adjusting the hydraulic pressure or electric power provided to a brake actuator depending on the degree of braking desired. In various embodiments, the BCU 120 controls the braking of the aircraft 100. For example, the BCU 120 controls various parameters of braking, such as manual brake control, automatic brake control, antiskid braking, locked wheel protection, touchdown protection, emergency/parking brake monitoring or gear retraction braking. The BCU 120 may further include hardware 117 capable of performing various logic using discreet power signals received from various aircraft systems. Referring again to FIG. 1A, the aircraft 100 further includes one or more brake assemblies coupled to each wheel assembly. For example, a brake assembly 118 is coupled to the outer wheel assembly 110 of the third landing gear 106 of the aircraft 100. During operation, the brake assembly 118 applies a braking force to the outer wheel assembly 110 upon receiving a brake command from the BCU 120. In various embodiments, the outer wheel assembly 110 of the third landing gear 106 of the aircraft 100 (or of any of the other landing gear described above and herein) comprises any number of wheels or brake assemblies.

Referring now to FIG. 1C, schematic details of the brake assembly 118 illustrated in FIG. 1A are provided. In various embodiments, the brake assembly 118 is mounted on an axle 130 for use with a wheel 132 disposed on and configured to rotate about the axle 130 via one or more bearing assemblies 134. A central axis 136 extends through the axle 130 and defines a center of rotation of the wheel 132. A torque plate barrel 138 (sometimes referred to as a torque tube or barrel or a torque plate) is aligned concentrically with the central axis 136, and the wheel 132 is rotatable relative to the torque plate barrel 138. The brake assembly 118 includes an actuator ram assembly 140, a pressure plate 142 disposed adjacent the actuator ram assembly 140, an end plate 144 positioned a distal location from the actuator ram assembly 140, and a plurality of rotor disks 146 interleaved with a plurality of stator disks 148 positioned intermediate the pressure plate 142 and the end plate 144. The pressure plate 142, the plurality of rotor disks 146, the plurality of stator disks 148 and the end plate 144 together form a brake heat sink or brake stack 150. The pressure plate 142, the end plate 144 and the plurality of stator disks 148 are mounted to the torque plate barrel 138 and remain rotationally stationary relative to the axle 130. The plurality of rotor disks 146 is mounted to the wheel 132 and rotate with respect to each of the pressure plate 142, the end plate 144 and the plurality of stator disks 148.

An actuating mechanism for the brake assembly 118 includes a plurality of actuator ram assemblies, including the actuator ram assembly 140, circumferentially spaced around a piston housing 152 (only one actuator ram assembly is illustrated in FIG. 1C). Upon actuation, the plurality of actuator ram assemblies affects a braking action by urging the pressure plate 142 and the plurality of stator disks 148 into frictional engagement with the plurality of rotor disks 146 and against the end plate 144. Through compression of the plurality of rotor disks 146 and the plurality of stator disks 148 between the pressure plate 142 and the end plate 144, the resulting frictional contact slows or stops or otherwise prevents rotation of the wheel 132. In various embodiments, the plurality of rotor disks 146 and the plurality of stator disks 148 are fabricated from various materials, such as, for example, ceramic matrix composite materials, that enable the brake disks to withstand and dissipate the heat generated during and following a braking action. As discussed in further detail below, in various embodiments, the actuator ram assemblies comprise a combination of electrically operated actuator rams (or electric brake actuators) and hydraulically operated (or pneumatically operated) actuator rams (or hydraulic brake actuators or pneumatic brake actuators).

Referring now to FIG. 2A, a braking system 200 (or a redundant braking system or a hybrid braking system) is illustrated, in accordance with various embodiments. Generally, the braking system 200 may be separated into a hydraulic braking subsystem 202 and an electric braking subsystem 204. Referring first to the hydraulic braking subsystem 202, the braking system 200 includes a hydraulic brake control unit 220, which is programmed to control the various braking functions performed by the hydraulic braking subsystem 202. The hydraulic braking subsystem 202 includes a hydraulic power source 222 configured to provide a hydraulic fluid to a primary brake control module 224 via a primary hydraulic line 226. A primary pressure transducer 228 senses the pressure of the hydraulic fluid and provides a signal reflective of the pressure to the hydraulic brake control unit 220 via a data circuit 230. In various embodiments, the hydraulic braking subsystem 202 includes a hydraulic fluid return 232 that is configured to return hydraulic fluid from the primary brake control module 224 to the hydraulic power source 222 via a return hydraulic line 234.

A secondary hydraulic line 236 fluidly couples the primary brake control module 224 to a brake assembly 218, similar to the brake assembly 118 described above with reference to FIG. 1A. More particularly, the secondary hydraulic line 236 is fluidly coupled to a hydraulic brake actuator 217 (or a plurality of hydraulic brake actuators) housed within the brake assembly 218. In various embodiments, a fuse 238 is fluidly coupled to the secondary hydraulic line 236 downstream of the primary brake control module 224. The fuse 238 acts as a shut-off valve or switch in the event the secondary hydraulic line 236 experiences a loss of pressure—e.g., in the event of a leak in the secondary hydraulic line 236 or the brake assembly 218—thereby preventing hydraulic fluid from continuing to flow to the secondary hydraulic line 236 and leaking out of the hydraulic system. A secondary pressure transducer 240 is fluidly coupled to the secondary hydraulic line 236 and electrically coupled to the hydraulic brake control unit 220 via the data circuit 230. In the event the secondary pressure transducer 240 senses a loss of pressure within the secondary hydraulic line 236, the hydraulic brake control unit 220 may, in redundant fashion, pass control of the braking system 200 to the electric braking subsystem 204. As illustrated, the secondary hydraulic line 236, the fuse 238, the secondary pressure transducer 240 and the brake assembly 218 are replicated for each of a plurality of outer wheel assemblies 210 and for each of a plurality of inner wheel assemblies 211 comprised within the braking system 200. Without loss of generality, in various embodiments, the hydraulic braking subsystem 202 also includes wheel speed transducers and brake temperature sensors, such as, for example, an inboard wheel speed transducer 242 and an outboard wheel speed transducer 243, and an inboard brake temperature sensor 244 and an outboard brake temperature sensor 245.

Referring now to the electric braking subsystem 204, the braking system 200 includes an electric brake control unit 250, which is programmed to control the various braking functions performed by the electric braking subsystem 204. The electric braking subsystem 204 includes an electric power source 252 configured to provide electric power to an electric brake actuator controller 254, which, for example, may be an inboard electric brake actuator controller or an outboard electric brake actuator controller. The electric power is provided to the electric brake actuator controller 254 via an electric power circuit 257. The electric brake actuator controller 254 is electrically coupled to an electric brake actuator 219 (or a plurality of electric brake actuators) that is housed within the brake assembly 218. In various embodiments, the electric brake actuator 219 includes or is connected to a control circuitry 256 configured to monitor various aspects of a braking operation. The control circuitry 256 may include, for example, a load cell configured to monitor the load applied via the electric brake actuator 219. In various embodiments, the electric brake actuator controller 254 provides force commands to the electric brake actuator 219, directing the electric brake actuator 219 to cause the brake assembly 218 to mechanically operate, thereby driving the brake assembly 218 to provide braking power. In various embodiments, the electric brake actuator controller 254 is coupled to the electric brake control unit 250 via a communication link 258. The communication link 258 may comprise, for example, a controller area network bus 260. Similar to the hydraulic braking subsystem 202, and without loss of generality, the electric braking subsystem 204 also includes wheel speed transducers, such as, for example, an inboard wheel speed transducer 262 and an outboard wheel speed transducer 263, or brake temperature sensors.

Referring now to FIG. 2B, the brake assembly 218 is described with further detail. As illustrated, the brake assembly 218 includes a pressure plate 215 configured to apply a compressive load against a brake stack or heat sink, which includes a plurality of brake rotors and a plurality of brake stators sandwiched between the pressure plate and an end plate. As described above, the brake assembly 218 includes the hydraulic brake actuator 217 (or a plurality of such hydraulic brake actuators) and the electric brake actuator 219 (or a plurality of such electric brake actuators). In various embodiments, the brake assembly 218 includes four electric brake actuators spaced at ninety degree (90°) intervals about the pressure plate 215 and four hydraulic brake actuators spaced at ninety degree (90°) intervals about the pressure plate 215, with each electric brake actuator and each hydraulic brake actuator spaced at forty-five degree (45°) intervals. Fewer or greater numbers of actuators, both electric and hydraulic, are contemplated within the scope of the disclosure.

During operation, a pilot or a co-pilot depresses a pilot brake pedal 270 or a co-pilot brake pedal 272, each of which is connected to a hydraulic brake position sensor 274 and to an electric brake position sensor 276. The hydraulic brake position sensor 274 generates a signal reflective of the pedal position that is transmitted to the hydraulic brake control unit 220 via a hydraulic brake sensor bus 278. The hydraulic brake control unit 220, if employed, then activates the hydraulic brake actuator 217 based on a current signal that is transmitted to the primary brake control module 224 via a primary brake control bus 225. Similarly, the electric brake position sensor 276 generates a signal reflective of the pedal position that is transmitted to the electric brake control unit 250 via an electric brake sensor bus 280. The electric brake control unit 250, if employed, then activates the electric brake actuator 219 based on a force request that is transmitted to the electric brake actuator controller 254 via the communication link 258. In various embodiments, an avionics system 282 is configured to employ one or both of the hydraulic braking subsystem 202 and the electric braking subsystem 204 via signals transmitted over a respective data bus 283. In various embodiments, an autobrake selector 284 is configured to employ one or both of the hydraulic braking subsystem 202 and the electric braking subsystem 204 via signals transmitted over an autobrake data bus 285.

The braking system 200 may operate in a fully hydraulic mode, employing only the hydraulic braking subsystem 202, or in a fully electric mode, employing only the electric braking subsystem 204. In addition, the disclosure contemplates, in various embodiments, the hydraulic braking subsystem 202 being employed as the principal braking system, while the electric braking subsystem 204 is employed as a backup braking system in the event a failure occurs with the hydraulic braking subsystem 202. The disclosure also contemplates, in various embodiments, the electric braking subsystem 204 being employed as a parking brake when the aircraft is at rest. In various embodiments, the hydraulic brake control unit 220 and the electric brake control unit 250 are configured to communicate with one another via an intercommunication bus 286. Such communication enables, for example, transfer of control from the hydraulic brake control unit 220 to the electric brake control unit 250 following a failure of the hydraulic braking subsystem 202. For example, in the event the hydraulic brake control unit 220 detects a leak of hydraulic fluid within the hydraulic braking subsystem 202, the hydraulic brake control unit 220 may communicate with the electric brake control unit 250 and transfer control of the brake system 200 to the electric brake control unit 250. Similarly, in the event the electric brake control unit 250 detects a failure within the electric braking subsystem 204, the electric brake control unit 250 may communicate with the hydraulic brake control unit 220 and transfer control of the brake system 200 to the hydraulic brake control unit 220.

The above disclosure provides for a hybrid braking architecture. In various embodiments, the architecture employs hydraulic power for normal braking and electric power for an alternate braking system or a parking brake system. The architecture provides a fully redundant braking system for normal pedal operated braking and for emergency braking. In various embodiments, the piston housing (e.g., the piston housing 152 referred to in FIG. 1C) is modified to accept four hydraulic actuators and four electric actuators, spaced equally and alternating between one hydraulic actuator and one electric actuator; though any number of actuators is contemplated by the disclosure. The equal spacing of forty-five degrees (45°) between alternating hydraulic and electric brake actuators allows for uniform force application on the brake stack when the hydraulic system is active or the electric system is active.

In various embodiments, the architecture is operated using pedals in the cockpit. This allows seamless activity and minimum pilot effort when, for example, the emergency system is engaged. The architecture is transparent for actuation (e.g., automated), although crew-alerting system (CAS) messages may be employed to inform the pilot that the emergency system (e.g., the electric braking subsystem) has become active. The hydraulic and electric brake control units are in constant communication using, for example, controller area network (CAN) communication links, such that when the primary brake control unit (either the hydraulic or the electric brake control unit) detects a loss of braking or other fault, the alternate brake control unit (either the hydraulic or the electric brake control unit) may take over control and operate the braking. In various embodiments, a switch may also be provided in the cockpit to allow the pilot to manually switch from the one braking subsystem to the other—e.g., the hydraulic subsystem to the electric sub system—depending on the failure and any other issues or faults occurring with the power supplies or other aircraft system degradations.

Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosure. The scope of the disclosure is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. Different cross-hatching is used throughout the figures to denote different parts but not necessarily to denote the same or different materials.

Systems, methods and apparatus are provided herein. In the detailed description herein, references to “one embodiment,” “an embodiment,” “various embodiments,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments.

Numbers, percentages, or other values stated herein are intended to include that value, and also other values that are about or approximately equal to the stated value, as would be appreciated by one of ordinary skill in the art encompassed by various embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable industrial process, and may include values that are within 10%, within 5%, within 1%, within 0.1%, or within 0.01% of a stated value. Additionally, the terms “substantially,” “about” or “approximately” as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. For example, the term “substantially,” “about” or “approximately” may refer to an amount that is within 10% of, within 5% of, within 1% of, within 0.1% of, and within 0.01% of a stated amount or value.

Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112(f) unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

Finally, it should be understood that any of the above described concepts can be used alone or in combination with any or all of the other above described concepts. Although various embodiments have been disclosed and described, one of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. Accordingly, the description is not intended to be exhaustive or to limit the principles described or illustrated herein to any precise form. Many modifications and variations are possible in light of the above teaching. 

What is claimed is:
 1. A braking system, comprising: a brake assembly; a hydraulic braking subsystem having a hydraulic brake actuator configured to operate the brake assembly; and an electric braking subsystem having an electric brake actuator configured to operate the brake assembly.
 2. The braking system of claim 1, wherein the brake assembly includes a pressure plate and an end plate and wherein both the hydraulic brake actuator and the electric brake actuator are configured to translate the pressure plate toward the end plate.
 3. The braking system of claim 2, wherein the hydraulic brake actuator is one of a plurality of hydraulic brake actuators configured to translate the pressure plate toward the end plate.
 4. The braking system of claim 3, wherein the electric brake actuator is one of a plurality of electric brake actuators configured to translate the pressure plate toward the end plate.
 5. The braking system of claim 4, wherein the plurality of hydraulic brake actuators comprises four hydraulic brake actuators spaced at ninety degree intervals about the pressure plate.
 6. The braking system of claim 5, wherein the plurality of electric brake actuators comprises four electric brake actuators spaced at ninety degree intervals about the pressure plate.
 7. The braking system of claim 1, wherein the hydraulic braking subsystem includes a hydraulic brake control unit configured to control operation of the hydraulic brake actuator.
 8. The braking system of claim 7, wherein the electric braking subsystem includes an electric brake control unit configured to control operation of the electric brake actuator.
 9. The braking system of claim 8, wherein the braking system includes an intercommunication bus between the hydraulic brake control unit and the electric brake control unit.
 10. The braking system of claim 9, wherein the hydraulic brake control unit is configured to transfer operation of the braking system to the electric brake control unit following a failure occurring within the hydraulic braking subsystem.
 11. The braking system of claim 10, further comprising a pressure transducer configured to sense the failure, via a loss or a reduction of fluid pressure, occurring within the hydraulic braking subsystem.
 12. The braking system of claim 9, wherein the electric brake control unit is configured to transfer operation of the braking system to the hydraulic brake control unit following a failure occurring within the electric braking subsystem.
 13. The braking system of claim 9, further comprising a hydraulic brake position sensor coupled to the hydraulic brake control unit and configured to sense a brake pedal position.
 14. The braking system of claim 13, further comprising an electric brake position sensor coupled to the electric brake control unit and configured to sense the brake pedal position.
 15. A redundant braking system for an aircraft, comprising: a brake assembly having a pressure plate, an end plate, a plurality of rotor disks and a plurality of stator disks interleaved with the plurality of rotor disks, the plurality of rotor disks and the plurality of stator disks disposed between the pressure plate and the end plate; a hydraulic braking subsystem having a hydraulic brake actuator configured to compress the plurality of rotor disks against the plurality of stator disks; and an electric braking subsystem having an electric brake actuator configured to compress the plurality of rotor disks against the plurality of stator disks.
 16. The redundant braking system of claim 15, wherein the hydraulic brake actuator is one of a plurality of hydraulic brake actuators spaced at equal degree intervals about the pressure plate.
 17. The redundant braking system of claim 16, wherein the electric brake actuator is one of a plurality of electric brake actuators spaced at equal degree intervals about the pressure plate.
 18. The redundant braking system of claim 15, wherein the hydraulic braking subsystem includes a hydraulic brake control unit configured to control operation of the hydraulic brake actuator and the electric braking subsystem includes an electric brake control unit configured to control operation of the electric brake actuator.
 19. The redundant braking system of claim 18, wherein the hydraulic brake control unit is configured to transfer operation of the redundant braking system to the electric brake control unit following a failure occurring within the hydraulic braking subsystem.
 20. The redundant braking system of claim 18, wherein the electric brake control unit is configured to transfer operation of the redundant braking system to the hydraulic brake control unit following a failure occurring within the electric braking subsystem. 